The invention relates to the control of phase currents of a three-phase inverter.
The inverter generates pulsed phase voltages which can assume a plurality of voltage values. For this purpose the inverter has, for each phase, a switching unit having a plurality of switching states by means of which the phase voltage of the phase is set to one of the voltage values in each case.
A problem arising for phase current control of a three-phase inverter is the possible occurrence of a zero sequence current. A zero sequence current of an inverter is the non-vanishing sum of the three phase currents. Zero sequence currents can in particular produce circulating currents which combine via electrical conductors, e.g. even ground conductors, connected to the inverter and can cause undesirable system oscillations. Particularly in parallel-connected inverters, circulating currents can occur which flow between the individual inverters and reduce the total output power of the parallel-connected inverters. Paralleling of a plurality of inverters is often used to interconnect the individual inverters to form an inverter having a higher total output power and availability.
The object of the invention is to specify improved control of phase currents of a three-phase inverter particularly in respect of reducing zero sequence currents.